Spencer joined the staff as defensive line coach in 2008 and was elevated to defensive coordinator in 2013. In a statement released Thursday, Oklahoma State coach Mike Gundy said he was "very appreciative for the 10 years of loyal service that Glenn Spencer gave to Oklahoma State."

Oklahoma State's offenses have been outstanding the past several years, but its defenses have lagged behind.

This season, the Cowboys hit a low when they lost 62-52 at home to Oklahoma behind Baker Mayfield's 598 yards passing. Oklahoma State also had poor defensive showings in losses to TCU and Kansas State that took the Cowboys out of the national championship picture. Oklahoma State finished the season seventh out of 10 teams in the Big 12 in scoring defense and eighth in passing defense.